Question: The drama club sold bags of candy and cookies to raise money for the spring show. Bags of candy cost $$8.50$, and bags of cookies cost $$2.50$, and sales equaled $$39.50$ in total. There were $7$ more bags of cookies than candy sold. Find the number of bags of candy and cookies sold by the drama club.
Solution: Let $x$ equal the number of bags of candy and $y$ equal the number of bags of cookies. The system of equations is then: ${8.5x+2.5y = 39.5}$ ${y = x+7}$ Since we already have solved for $y$ in terms of $x$ , we can use substitution to solve for $x$ and $y$ Substitute ${x+7}$ for $y$ in the first equation. ${8.5x + 2.5}{(x+7)}{= 39.5}$ Simplify and solve for $x$ $ 8.5x+2.5x + 17.5 = 39.5 $ $ 11x+17.5 = 39.5 $ $ 11x = 22 $ $ x = \dfrac{22}{11} $ ${x = 2}$ Now that you know ${x = 2}$ , plug it back into $ {y = x+7}$ to find $y$ ${y = }{(2)}{ + 7}$ ${y = 9}$ You can also plug ${x = 2}$ into $ {8.5x+2.5y = 39.5}$ and get the same answer for $y$ ${8.5}{(2)}{ + 2.5y = 39.5}$ ${y = 9}$ $2$ bags of candy and $9$ bags of cookies were sold.